You can start with a DC R measurement. If they seem fairly precise at DC, that's a good sign that they were intended to be so there and beyond. The RF/HF is of course a different story, but good LF/DC is necessary before you even worry about going up. Most typical terminators that I've seen are around +/- 5%, so nothing special. if you see say, one percent or better, then maybe they're pretty good - at LF/DC at least.

You can check them at RF/HF too, if you have the right gear. The type/grade of connector is a big factor too - if you're talking about BNC only, it's not a big deal.

Ed

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All that HPAK have to say is here:

They list both BW and VSWR as 'unknown'.
I read it as saying it was only ever intended for use at ~100MHz as part of the performance tests for the 54620 series 'scopes and perhaps some older ones?

Don't expect great HF performance in BNC terminators. In its fairly common use - to make a 1 meg parallel some tens of pF scope input look kind of like 50 ohms - you'll always have the unavoidable capacitance in shunt. It will be be 50 R just fine at low frequency, but it's not at all equivalent to a true 50 R resistive RF/microwave system. No matter how good the terminator is, the problem is in the scope's native high-Z input structure.

Ed

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Hello Jared,

There is a BNC one from RADIALL specified to 1 Ghz , reference R405005

Best regards
Eric

Hi , there is also a SUHNER 50 ohm feed through termination ,?
BNC specified to 1 GHz mod. 6701.01.B

Regards
Maurizio IZ1MDJ

?

For use with a typical 100MHz scope? with a 1Meg input?and (say) a parallel input capacitance of about 18pF, the ideal 50R terminator would have a 50R resistor and a negative capacitor in parallel with it with a value of -18pF.

As negative caps aren't realisable with passive parts, the next best thing to do is to add some inductance to the 50R resistance to try and mimic a -18pF capacitor over as wide a bandwidth as possible. I suspect that some terminators designed for scopes will do this to some degree.

Compared to terminating with a perfect 50R resistor, this should give a lower VSWR over a fairly wide bandwidth when the (slightly inductive) terminator is added to the scope input as the inductance will offset most of the 18pF capacitance of the scope over quite a wide bandwidth.

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Typically anything with a BNC connection is only rated to 1 GHz, ie. HP 355 attenuators. ?I have pushed a BNC cable to 1.5 GHz, but that is as far as I would go with it.

That may be true for 50 Ohm but do not try it with the 75 Ohm versions!
BNC/TNC have the same inner pin dimensions and 'fix' the impedance by changing the dielectric insert dimensions in the mating area but 'N' type have a different diameter centre contact!

We found the other issue with BNC at higher frequencies is that, again possibly due to the method of retention, they seem to fall off much faster over time with use, the inner contact sleeves seemed to get worn/distorted more. Perhaps due to more 'brute force' being used to overcome misalignment during connection but the TNCs seemed to survive much better 'in the field'. This last, in the case of Radio Astronomy, was both a figurative and literal term!

50R BNC / TNC and 50R N types have the same outer conductor inner diameter and center conductor outer diameter BUT the tapered and reduced pin diameter is larger on N types than BNC / TNC . Thus while you can push a N male into a BNC or TNC female it will stress the female contact and my cause permanent deformation depending on the exact connectors.

BNC / TNC female is designed to mate with a 0.052 to 0/053" diameter pin Ntype is 0.063-0.066" diameter.

See MIL-A-55339A

Robert G8RPI.

BTW it's? Paul Neill and Carl Concelman who were desiners at Bell Labs. While credited with various connector designs I'm pretty sure the attribution of the N and BNC to their names is coincidental and happened long after the introduction of the connectors.

Older docunemts refer to N as Naval but it was almost cetainly just a alphabetic sequence. T/BNC is threaded or Bayonet N Compact in older references. This make more sense than acorporation naming a part after the designer(s) particuarly as when desigined there is no indication of how popular the part may become.

I know of at least one case of theis re-naming after the event. This is the standard for rack mounting avionics equipment. It's known as ATR racking. In the first edition of the specification, ARINC 404 ATR was defined a Air Transport Radio racking. At revision A it was re-defined as Austin Trumbull Radio racking in recognition of the main designer. PArt of ARINC 404A appendix 1 is below.

"GENERAL
The material in this appendix is presented in order to preserve important background regarding the viability of the ATR
concept pioneered by Austin F. Trumbull of United Air Lines (now retired). This importance is not so much related to the
personages involved as it is to the painful, deliberative process through which the present 404A rack concept has evolved
to its present day form.
BACKGROUND
Coincident with the hiring of an ARINC Staff Engineer in the year 1939, the ARINC Board of Directors officially
directed ARINC to accept the responsibility, for the airlines, to coordinate Industry design and development work. This
was the official beginning, within ARINC, of a continuing program identified loosely as the “Air Transport Radio”
development program. Thus, with this introduction of radio racking and equipment box size standards in early 1940, it
was natural that these racking standards were loosely referred to as “ATR” Standards. With the eventual publication of
ARINC Specification No. 404 embracing these original 1940 standards some sixteen years later (May 1, 1956) it was
natural that the acronym “ATR” would have been explained as meaning “Air Transport Radio” (see Section heading of
Section 1.0 and line 12 of Section 1.1 of ARINC Specification No. 404, Page 7, dated May 1, 1956).

founding of AEEC that this definition attributed to the acronym “ATR” was completely erroneous, irrelevant, and
incorrect, and can be attributed only to a typographical error (noting that ARINC employed the first full time
stenographer on May 14, 1939 and she had obviously not yet become familiar with these complicated terms!)
Accordingly a supplement to 404 was proposed to correct that typographical error. Excerpts from that supplement
follow:
To complete the historical record of the early developments of the ARINC “ATR Racking System” this
Supplement will, in addition of decreeing a change in the meaning of the acronym, also serve to add an
Appendix 2 - “Chronology of the ARINC Racking System,” to be recorded in Specification 404.
Change to ARINC Specification No. 404 to be Made by this Supplement No. 5 dated April 15, 1967
It is hereby decreed, retroactive to April 15, 1940, by action of the Airlines Electronic Engineering Committee
on April 12, 1967, that Section 1.0 and 1.1 of ARINC Specification No. 404 dated May 1,1956, will have been
modified by striking out the meaning of “ATR” given in the heading of section 1.0 and in the fourth sentence of
Section 1.1, replacing it by the correct term. Specifically, where the term “Air Transport Radio” is used, it shall
have been replaced by the words “Austin Trumbull Radio” heretofore and hereinafter, which by AEEC decision
will have been made to have been “traditional” since April 15, 1940."

Note ARINC 404 was the basis for MIL-C-172 Which does not mention ATR or Austin.

Robert G8RPI.

Well, BNC connectors have more mechanical play (by design) than TNC. You can see that on a VNA when you wiggle the BNC. I therefore rate TNC higher than BNC.

Wilko

I like high quality BNC RG-223 cables for lab bench work but they are hard to find!

Lots of junk out there.

Hi Jeff,
a 0.01" (10 thou) delta does not sound like much on it's own, but in this case it is 20% oversize, That's like trying to screw a M10 nut onto a M12 bolt.

At worst case design limit it is 0.011 to 0.014" oversize.You will damage a good quality TNC/BNC female by pushing a N male into it.

On naming, I've no reason to be jealous but very few military connectors are named after their designers. The truth is probably lost in time. I've never been able to find any contempary documentation to support either way.